a:) with the playground pleasantry of the week (arse head, poo face, shit neck.....)
b:) to offer him a bite of your penguin bar
c:) to swap World Cup '90 stickers
d:) to show him some animal you fried with a magnifying glass

Engage in conversation, all the time maintaining eye contact, never giving away your true intentions. Smile a lot, crack a joke or two, but never, ever glance at the nipple. This is of the utmost importance. Any hint that you are about to deleiver the NT could be a serious threat to your health. As the conversation reaches exhaustion, remove your hand from your pocket as if to take something out of it. Then, look at a point over your victims shoulder, an object in the distance. Your victim will note your distraction and turn his head to see what you're looking at.

As he turns his head, thrust your hand forward sharply into his chest, if you're right handed, go for the left nipple with your thumb and first two fingers. Finding the exact location of the nipple is not that important, as it will be usually be well within your 'twist zone'. Now, before your victim realises what the hell is going on, twist that nipple as hard as you can.

The response to this random, unprovoked attack is usually a severe beating at the hands of the victim. This is thoroughly deserved and should be absorbed with grace and dignity. Remember, if things get out of hand, you always have that ruler handy.....